Barrel spring



Ma rch18,1969 'WASAWA Z'-* 3,433,011

BARREL SPRING Filed April 28, 1967 FIG. I FIG. 2

TORQUE TORQUE REVOUJTIONS OF BARREL Q FIG. 3

0525mm Lu United States Patent Oflice 3,433,011 Patented Mar. 18, 1969 7 Claims Int. Cl. G04b 1/16 ABSTRACT OF THE DISCLOSURE A barrel spring, having a lower elasticity at the reflex zone in proximity to the outer extremity of said spring than other plain part thereof.

This invention relates to improvements in and relating to barrel springs for timepieces.

It is observed that the conventional barrel spring represents a sudden and disadvantageous rise in its output torque when it is loosened from its fully wound-up con dition, and indeed, at the start of the loosening step for driving a timepiece movement. This sudden rise of the output torque can be well and clearly observed not only in the course of a torque test of the barrel spring on a test bed, but also during the practical time-keeping operation of the timepiece fitted with such spring barrel. This torque rise, if it happens to take place, will naturally disturb the regular time-keeping operation of the springdriven timepiece and may constitute a grave problem in the manufacture of high precision time-keeping movements in compliance with recent demands.

It was now found upon our profound experiments that the true and real cause of the sudden torque rise of the above kind is attributable to the provision of a conventional reflex zone positioned in proximity to the outer extremity of the barrel spring, said zone being the joining point, and its related area, defined between the outer end curved area extending a specific small distance and the general S-curve extending over nearly the overall length of said spring.

In the state of fully wound-up or tightened condition of the barrel spring, the aforementioned reflex area is subjected to a considerable elastic deformation by forcibly having a curvature substantially equal to that prevailing in the outer peripheral curve of the tightly coiled barrel spring as a whole, thus accumulating in the said zone a considerably localized, large amount ofrepulsive energy. As ascertained by our experiments, this accumulated repulsive energy is released suddenly to a large extent at the commencement of the loosing course of the tightened barrel spring for providing the necessary energy to drive the timepiece movement fitted with the spring for carrying out the proper time-keeping function of the timepiece. This sudden release of the accumulated energy is brought about especially during the first one revolution of the barrel.

It is therefore the main object of the present invention to provide a barrel spring, capable of obviating the aforementioned conventional drawback.

It is another object of the invention to provide a barrel spring of the above kind which has highly improved torque characteristics.

In order to realize the aforementioned objects, it is proposed by the present invention to provide means for re ducing the elasticity in the said reflex zone of the barrel spring. The first way for this purpose is the provision of such mechanical means for reducing the cross-sectional area through a barrel spring part at the geometrical reflex point and its related area. This mechanical means may be in the form of a longitudinal slot formed along the central axis of the barrel spring and extending within said area. This slot may be replaced by a series of small round openings bored through the spring along said axis and at regular intervals. Or alternatively, a longitudinal recess may be formed along one or each of the side edges of the spring.

The second way serving for the desired purpose is to provide a localized heat treatment to the said reflex zone of the spring. A recommended measure to do this is to reduce the elasticity to 60-30% based upon the normal value, assuming 100%, which is had by the main part of the spring. Naturally, the above-specified figures may be subjected to modification, depending upon the nature and kind of spring material, the sizes of the spring and the degree of curvature in the outer end portion as well as the main part of the spring.

These and other objects, features and advantages of the invention will become more specific when reading the following detailed description of the invention by reference to the accompanying drawings illustrative of several embodiments of the invention disclosed only for illustrating purpose and thus in no limiting sense thereof.

In the drawings:

FIGURE 1 is a schematic diagram of driving torque provided by a conventional barrel spring plotted in a random scale against the number of revolutions of barrel.

FIGURE 2 is a similar diagram to FIGURE 1, wherein however the improved barrel spring according to this invention is tested.

FIGURE 3 is a top plan view of a barrel spring substantially developed for the illustration of several curvatures embodied therein.

FIGURE 4 is an enlarged view of a part of the spring shown in FIGURE 3, illustrating the outer extremity of said spring including the reflex zone thereof.

FIGURES 5-7 are top plan views of respective outer extremities of several embodiments of barrel spring, embodying the principles of the invention.

FIGURE 8 is a similar view to FIGURE 5, illustrative of a modification from the embodiment shown therein, especially for the purpose of showing dimensional particulars.

Now referring to a characteristic torque curve of conventional barrel spring shown in FIGURE 1, the curve represents a sudden rise of torque shown at A. As already referred to, the main object of the present invention is to obviate this sudden rise. In comparison therewith, the improved torque curve obtained from an embodiment .of the invention and shown in FIGURE 2 represents no such torque rise.

In FIGURE 3, a barrel spring is shown in its substantially developed plan view, wherein the lowermost end represents the inner end of the spring, while the upper part shown corresponds to the outer end of the spring, generally denoted at 10.

The outer end portion of the spring 10 including the reflex zone at issue is shown by encircling a small dotted circle 11 in FIGURE 3, which part is shown more in detail in FIGURE 4.

In FIGURE 4, a reflex point is shown at 13 which is defined by a curved end, extending within a straight distance at L, on the one hand, and by S-curved main part (shown in FIGURE 3) of the same spring 10, on the other hand. In FIGURE 4, there is shown a small dotted circle 14 which includes the reflex zone shown as that denoted M in each of FIGURES 5-7.

As conventionally, the spring 10 is reinforced by attaching fixedly thereto a reinforcing strip 15 as 'by spot welding at 16.

In FIGURE 5, an elongate rectangular slot 17 is cut through the material of the spring, so as to reduce the cross-sectional area of or the elasticity in the zone M in comparison with that prevailing in other main or plain part of the spring. The results shown in FIGURE 2 were obtained with use of the embodiment shown in FIGURE 5.

In the second embodiment shown in FIGURE 6, elongate notches 18 and 19 are formed along the both edges of the spring within said zone M, in place of the slot at 17 in the foregoing embodiment.

In FIGURE 7, a slightly wider elongate notch is provided only at one side of the spring within said zone M.

In FIGURE 8, a modification from the embodiment in FIGURE is shown, especially for the purpose of dimensional illustration.

In this modification, reinforcing strip a is of 1.2 x 0.1 X 3.5 mm. while the spring 100 is of 1.55 x 0.074 x 310 mm. The reflex point is shown at 13a. Other several reference symbols are shown with similar one attached each with a suffix a. The width of slot 17a may be increased, if necessary, to about 1 mm. with reduced slot length.

Example of heat treatment A commercially available barrel spring strip, of a trade name PHINOC and a chemical composition, percent by weight, of:

Si less than 0.50.

P less than 0.03.

S less than 0.03.

Co higher than 40.00. Fe rest.

was cut into sizes. The longitudinal dimension of the spring amounted to 30-40 cm. for gentleman timepieces and about cm. for lady timepieces, respectively. Upon mechanically rolled up at the inner extremity so as to be slid over a 'barrel arbor, not shown, bored :1 conventional hanger opening, not shown, through the inner end portion and attached fixedly with a reinforcing strip 15 or 15a onto the outer end portion as shown in FIGURES 5-8, as by welding at 16 or 16a, the spring was mechanically deformed so as to take a general configuration as shown in FIGURE 3. Then, the shaped spring was locally annealed at the aforementioned zone M, yet including the outer end portion L for ease of heat treatment, at 1100 C. or higher for 10 minutes, and then gradually cooled down to room temperature. The thus heat-treated stock was placed in a barrel case, with a length of inner spring end kept exposed. Then, the spring with barrel was subjected to an aging step, as conventionally, at 500 C. for 2 hours, and cooled gradually down to room temperature, thus becoming ready for use.

This finished barrel spring represented a favorable 4 torque charactertistic curve similar to that shown in FIGURE 2.

If necessary the annealing step may be carried out in advance of said mechanical deformation step, yet with equal superior results.

Although not shown, a series of round holes may be formed along the longitudinal axis of the spring within said zone M, for the same purpose.

In place of the provision of said slot or notches, a local heat treatment may equally be employed for reducing the elasticity.

What we claim is:

1. A barrel spring comprising a substantially S-sl1apcd main part and a reversel curved outer end, thereby defining a reflex point at the intersection of said both curves wherein the improvement comprises the provision of a longitudinal zone including said reflex point and extending over a predetermined length, the elasticity in said zone being lower in its value than that prevailing in substantial part of said main spring part, for substantially obviating a possible torque rise as otherwise appearing at the initial stage of energy release when said spring is loosened from its fully tightened state for drive of a timepiece.

2. Barrel. spring as set forth in claim 1, wherein the improvement comprises the provision of cross-section re ducing means.

3. Barrel spring as set forth in claim 1, wherein said means is a longitudinal slot cut through the material of said spring and extending over substantially the length of said zone.

4. Barrel spring as set forth in claim 2, wherein said means comprises an elongate side recess extending substantially over the length of said zone.

5. Barrel spring as set forth in claim 2, wherein said means comprises two elongate side recesses, each extending substantially over the length of said zone.

6. Barrel spring as set forth in claim 2, wherein the improvement comprises a series of separated round openings bored through the material of said spring and arranged substantially over the length of said zone.

7. Barrel spring as set forth in claim 2, wherein said zone has been subjected to an annealing at a temperature higher than 1100 C. for a period of 10 or longer minutes.

References Cited UNITED STATES PATENTS 1,677,045 7/1928 Odom 5887 X 1,952,713 3/1934 Kelch 58-87 X FOREIGN PATENTS 1,058,237 3/1954 France.

1,176,728 4/1959 France.

RICHARD B. WILKINSON, Primary Examiner.

GEORGE H. MILLER, In, Assistant Examiner.

US Cl. X.R. 3l7--36; 336174 

